Sleep-related vehicle accidents are prevalent early morning, especially in younger drivers. In two independent studies following a night of either restricted or nil sleep, young experienced drivers drove for 2h (0600-0800h) continuously in an immobile car on an interactive, computer-generated dull and monotonous roadway. This followed ingestion (at 0530h) of 200mg caffeine (=2-3 cups coffee) Vs placebo, counterbalanced, double blind. Driving incidents (lane drifting), subjective sleepiness, and 4-11Hz EEG activity were logged. Study 1 (sleeping 0000-0500h): caffeine significantly reduced incidents and subjective sleepiness throughout the 2h drive, and EEG power for the second 30min period. Study 2: (no sleep) sleepiness profoundly affected all measures, and driving was terminated after 1h. Nevertheless, caffeine significantly reduced incidents for the first 30min and subjective sleepiness for the hour. This caffeine dose, feasibly taken via coffee, effectively reduces early morning driver sleepiness for about 30min following nil sleep, and for around 2h after sleep restriction. (A)
Abstract